1. Field of the Invention
This invention relates, in general, to MSI and LSI technology wherein high density integrated circuits are packaged and utilized in high speed data processing systems and relates, in particular, to the provision of sufficient cooling of such high density integrated circuit packages to maximize the capabilities of such MSI and LSI circuits.
2. Description of the Prior Art
As explained in detail in the U.S. Pat. No. 3,946,276 issued to Braun et al on Mar. 23, 1976, entitled, "Island Assembly Employing Cooling Means for High Density Integrated Circuit Packaging" and assigned to the assignee of this present application, present high speed computer systems require high density integrated circuits and a packaging technology to fully exploit the capabilities of such circuits. As shown and described in the subject patent, a plurality of pluggable integrated circuit (I.C.) packages, receptacles or connectors for receiving such packages, and interconnecting media were mounted on a cooling frame to form an "island." This island was made, more specifically, of a plurality of I.C. packages of the leadless variety, having a conductor metallization on an insulated carrier and an integrated heat sink plate, which were placed in the connectors positioned on a supporting medium, such as a printed circuit (p.c.) board, and pressed down by suitable clamps against the p.c. board and against the contacts in the connectors to make the electrical connection with other circuitry. These clamps also engaged a bracket which formed part of a cooling frame, and the I.C. packages, interconnecting medium, and connectors were supported thereon. This frame incorporated a hollow continuous tubing, arranged in a serpentine manner, through which a liquid coolant was pumped to carry away the heat generated by the I.C. packages. Heat transfer was accomplished by permitting the metal heat sink plates to make thermal contact with the metallic cooling frame.
While the foregoing described patented island assembly and cooling system thereof solved the basic problem of cooling high powered high density IC packages which could no longer be sufficiently cooled by moving air as conventionally done theretofore, it has been found that the system could be improved in a number of ways and it is, therefore, the main objects of this invention to:
1. Provide a means for effectively managing the heat generated by such high powered high density MSI and LSI chips so as to be usable in high performance circuits, such as in a current mode logic system,
2. To do this with maximum reliability, and
3. To do this cost effectively.
Meeting the foregoing objects, a primary improvement over the patent invention lies in elimination of the pump for pumping the liquid coolant, the serpentine tubing, heat exchangers for cooling the liquid, and all other equipment necessary for a somewhat typical refrigeration circulation system with attendant problems, such as leakage especially at the interconnections between the cooling system and the island frame, problems of corrosion with liquid flowing within metallic tubing etc, and vibration attendant to the pumping of liquid coolant through a frame such as in the prior art. It also must be realized that in a system with a plurality of islands, each island must be provided with a quick disconnect coupling so that an island can be withdrawn and replaced if necessary without the entire system being down and these quick disconnects are costly. This improvement was accomplished by the introduction of heat pipes into the cooling frame. These heat pipes, forming a structural member of the frame, serves to dissipate the heat generated by these I.C. packages without all of the aforementioned equipment necessary for liquid cooling. In this invention the heat pipe itself collects the heat and moves it by change of phase without motors or pumping equipment or fittings or otherwise and being a change of phase type operation, it is the most effective transfer of heat possible localized on each island with no loss of efficiency through mechanical motion and obviates the need for many moving parts which increases system reliability, reduces periodic maintenance and offers hardware cost savings in that the heat pipe plus the frame is less than the heat pipe plus the tubing motors, etc.
Finally, one more advantage of the present invention over the prior art in the utilization of the heat pipes with the localized air flow cooling thereof gives the system increased flexibility in that a heat pipe island containing current mode logic devices as a unit can be easily connected to an existing air cooled system by simply connecting the island to the existing air flow system, since there is no water pump, no external blower systems, etc. required.
Another improvement is the introduction of a modularity concept of sub-islands, together forming an island, yet without sacrificing I.C. packaging density. This modularity permits the removal and testing of only a portion of an entire island and a replacement of some portion thereof, if necessary, without removing the entire assembly. Perhaps the most important factor is the cost saving aspect of the modularity concept in connection with testing is the time involved. It takes less time to satisfactorily test, for example, six modules each containing a given number of IC packages then it does to test the same total (given number X 6) of IC packages on a large island board.
The introduction of the modularity concept reduces hardware costs in the event a full island is not required and secondly, the modularity increases the total yield of P.C. boards in that a defect in a large board requiring its rejection is more costly than a defect in a small board. Thus, as for example, its more cost effective to utilize six small P.C. boards than to utilize one large board as in the case of the prior art. It can also be appreciated that utilization of smaller P.C. boards allows freedom to partition into standardized modules, as for example, standardizing a module of input/output electronics to interface with peripheral equipment which may never need changing whereas the rest of the island may be subject to change depending upon customer needs. Thus, it should be clear that modularity does not simply mean cutting one large island into a number of sub-islands but modularity means taking advantage of a number of possibilities such as standardization (and theretofore a mass production cost reduction) of parts of the heretofore larger board.
Going further, with the introduction of the modularity concept, another improvement becomes apparent and that is in the means for clamping the I.C. packages into their connectors. These clamps remain latched even though one of the sub-islands is disconnected from the cooling frame so that removal of one of the sub-islands from the cooling frame does not in any way affect the relationship of the I.C. packages and their respective connectors. This, of course, means, as aforesaid, that any sub-island is capable of being removed as an integrated unit, repaired and/or tested and replaced without disturbing the other sub-islands.
Still another improvement over the patented invention lies in the aforesaid means for clamping the I.C. packages into their respective connectors. In the patented invention, first of all, the connectors for pressing the I.C. packages into the connectors formed part of, or were attached to, the cooling frame. The patented clamping means were attached at one end and pivoted about one portion of the cooling frame and locked into an adjacent portion of the cooling frame. This pivotal movement introduced a rubbing, albeit minute, of the I.C. package against the connector, but when one considers that the leads for the I.C. packages and the connectors are relatively thinly plated, this rubbing contact had a tendency to damage the connections and thus led to the possibility of an open connection between the I.C. package and the leads of the connector.
Thus, a concomitant improvement in the present invention is in the clamping means for clamping the I.C. packages into the connector in that the pressure actuated by the clamping means is in one direction only, i.e., downward, against the top surface of the I.C. packages to avoid the aforementioned rubbing or sliding effect on the contacts.
Also, with the introduction of the modularity concept and the heat pipes, still another improvement lies in a second clamping means for clamping the sub-island to the heat pipes and frame. This clamping means is independent of the aforesaid IC package clamping means and is simple to operate, utilizing only a screw driver or similar tool to latch and unlatch the sub-islands from the heat pipes.
This second clamping means, too, is a significant improvement over the prior art in that the clamp means first of all eliminates the screw attachment requirements of the patented invention where the P.C. board was attached by screws to the frame sections but secondly, the fact that this clamping means, being integral, eliminates the possibility of loose parts accidentially dropping onto the I.C. packages and conductors causing a short circuit and possible damage to the components of the system.
Other improvements over the prior art will become apparent to those skilled in the art after a study of the following summary and description of the preferred embodiment.